Exposing the Cast Signing Algorithm

1. Exposing the Cast Signing Algorithm in cdm core.
2. Update core Cast tests to use new core CDM Cast signing API.

Bug: 279671867
Bug: 279672538
Change-Id: Ia73c4b5e6dd61edf790bca97a321881d310e7a99

libwvdrmengine/cdm/core/include/crypto_session.h

@@ -347,6 +347,11 @@ class CryptoSession {
   virtual CdmResponseType LoadOtaProvisioning(bool use_test_key,
                                               const std::string& response);
 
+  // Cast specific generate signature method.
+  virtual CdmResponseType GenerateRsaSignature(const std::string& message,
+                                               std::string* signature,
+                                               RSA_Padding_Scheme scheme);
+
  protected:
   // Creates an instance of CryptoSession with the given |crypto_metrics|.
   // |crypto_metrics| is owned by the caller, must NOT be null, and must
@@ -385,8 +390,6 @@ class CryptoSession {
   // Note:  This function will lock the global static field lock in write mode.
   bool SetUpUsageTable(RequestedSecurityLevel requested_security_level);
 
-  CdmResponseType GenerateRsaSignature(const std::string& message,
-                                       std::string* signature);
   size_t GetMaxSubsampleRegionSize();
 
   bool SetDestinationBufferType();